In the remote Alaska wilderness, some 3,800 miles from Pyongyang, North Korea, the United States' last line of defense against a nuclear warhead from North Korea or Iran stands ready to attack.

Fort Greely, Alaska, a World War II-era Army base that was reopened in 2004, is America's last chance to shoot down a missile from overseas that could be carrying a nuclear weapon. Its underground steel and concrete silos house 26 missile interceptors that have, in tests, a 50 percent success rate.

The 800-acre base is located some 100 miles southeast of Fairbanks, in the looming shadow of Denali. It is one of only two missile defense complexes in the country. The other, Vandenberg Air Force Base in California, houses four interceptors that are used for testing and "backup," according to defense officials.

In March, as the North Korean crisis began to heat up, President Obama ordered another 14 interceptors be sent to Greely, bringing its arsenal to 44 from 2017.

Concern about North Korea heightened this week when the Defense Intelligence Agency released a document that concluded with "moderate confidence" that North Korea might have a nuclear weapon that's small enough to be placed on a ballistic missile. But the agency also said the reliability of a North Korean missile would be low.

Greely is equipped to handle the current threat, which is seen as slight, according to Leon Sigal, an expert on North Korea at the Social Science Research Council in New York.

"If all it has to worry about is a single missile coming at it, chance it could kill it. If you fire six missiles at one time... and if one gets through, your whole day is ruined.... The problem is sooner or later North Korea will improve its missile ranges, so the question you have to ask is will our anti-missile capabilities make sufficient progress so it could work against a more robust threat?" Sigal said.

"What we've got at Greely is of some limited utility. It's better than nothing," he said.

The U.S. military, however, confident that Greely is poised to swat away any missile threat.

"Basically central Alaska was an ideal spot because of the geometry you'd have to conduct a hit-to-kill intercept from a country like Iran or North Korea," said Ralph Scott, spokesman for the Missile Defense Agency in Alaska.

"Alaska is like the top of the world, and the only way you can view it as a missile defense benefit would be to look at a globe. You can see the routes the missiles from North Korea and Iran would take to get to the U.S. Having the system there in central Alaska would give you that geometry," Scott said.

The base at Fort Greely is desolate and spare, with one highway that rolls into and out of the base connecting it to a rugged Alaskan landscape. As the base's spokeswoman, Deborah Coble, pointed out, the nearest stoplight is 100 miles away.

The base was used in the years after World War II to train soldiers in cold climate-warfare. Soldiers now stationed at the base still test cold-weather uniforms, layered with synthetic and engineered fibers, for the Army.

"Travel to areas with standard day-to-day services can be treacherous," Coble said. "Temperatures can reach from 60 below zero and colder in winter to the high 80s to low 90s in summer. Winds can reach over 80 (miles per hour). Fort Greely is truly the 'Home of the Rugged Professional.'

Today, Fort Greely's sole purpose is missile defense, and its only occupants are staff to operate and maintain the missiles, their software, and the base's operations. The population is usually about 1,450 people. Most are contractors charged with maintaining the technology, and base support staff. The crew includes only 40 active duty Army troops and 160 members of the National Guard's 49th Missile Defense Battalion.

The interceptor silos are spread across two missile fields on the base. In the event of a missile launched from the other side of the world, clam shell-like doors at the top of the silos would shoot open and the interceptor would rocket more than 100 miles into the sky at speeds of 18,000 miles per hour, according to Scott.

When the 54-foot-long interceptors reach the right altitude, the interceptors launch the attached 140-pound "kill vehicle" at the warhead, Scott explained. The two collide, taking down the nuclear warhead.

"There are no explosives. It's all done by kinetic energy," he explained.

Alaska's Fort Greely Last Chance to Stop Incoming Nukes

"It's hit-to-kill technology," said Rick Lehner of the U.S. Missile Defense Agency. "What it does is, you're colliding the kill vehicle directly with the warhead, and just the sheer force of the collision happens very high in space."

Tests of the technology, however, have shown problems with the interceptors and their effectiveness in taking down another missile. While the Alaska interceptors have never been tested, the ones at Vandenberg have been tested with about a 50 percent success rate.

"We've had 15 tests, and eight have had successful intercepts. Seven did not, but of those seven only three were actual misses and the other four came from problems with quality control or software issues," Lehner said.

"Based upon what we learn from the failures, we've incorporated fixes into the silos in Alaska and California," he said. "We have very, very high confidence in their ability to perform."

Congress has also asked the Defense Department to look into placing a missile defense system on the East Coast, though Lehner insisted that the Alaska base would be able to protect the entire country from a missile attack.

As rhetoric from North Korea has grown more belligerent in recent weeks, missile defense systems around the world are prepared for any kind of launch, according to the Department of Defense. That includes defenses against short- and mid-range missiles aboard battle ships in the Pacific as well as radar and ground systems in Japan and Guam.

But the interceptors at Fort Greely are specifically designed for long range missiles, known as an Intercontinental Ballistic Missile or ICBM, currently in development in North Korea and Iran.